Cache

Question 1

Hardware prefetching

Answer 1

using hardware to predict blocks of data that will be used soon and fetch it before it is used.

Question 2

What to prefetch?

Question 3

When to prefetch?

Question 4

Write-through

Answer 4

When there is a cache hit for an address that needs to be written to, the value is written in the cache and the lower levels of memory

Question 5

Write-back

Answer 5

When there is a cache hit, the block in cache is written and also stored in the Write Back Buffer (WBB). It’ll be written to lower levels of memory when there is a read of the block.

Question 6

Replacement Policies

Answer 6

Put blocks into the cache speculatively. Read addresses from a lower level.
exp.
next block prefetching: getting the next block when the current block access has a miss
binding: prefetch data in registers only
non-binding: prefetch data in cache only
only prefetch when there is dead data in the cache

Question 7

Timeliness

Answer 7

start prefetch sufficiently in advance

Question 8

Coverage

Answer 8

prefetch as many as possible

Question 9

Accurate

Answer 9

predict data to prefetch that will be used soon and not fill the cache with unnecessary or non useful data and avoid eviction of useful data!

Question 10

Correlating Predictor

Answer 10

a large table of addresses with a miss

Question 11

Stride Prefetcher

Answer 11

Uses direct map cache. Every address in the table has an associated stride value.
The new address - old address of the same tag = actual stride.
If no match, update stride state.
The new address + stride in table (aka predicted stride) = prefetch or not.